With the current tendency that electronic devices use higher frequencies, a capacitor having better impedance characteristics in a high frequency range than those of the conventional configuration is required also for a capacitor as one of the electronic parts. In order to meet such a demand, various solid electrolytic capacitors using a conductive polymer having high electrical conductivity as the solid electrolyte have been discussed.
Moreover, recently, a small size and a large capacity are strongly demanded for a solid electrolytic capacitor to be used around a CPU of a personal computer. Furthermore, corresponding to the tendency toward higher frequencies, lower ESR (equivalent series resistance) and lower ESL (equivalent series inductance) with good noise removal and transient response properties are required. For responding to the demands, various discussions have been made.
Among them, the periphery of the anode electrode will be discussed first. FIG. 20A is a front cross-sectional view showing the configuration of a conventional solid electrolytic capacitor of this kind, FIG. 20B is a side cross-sectional view on the 20B-20B cross section in FIG. 20A, and FIG. 21 is a plan view of the solid electrolytic capacitor before externally mounting. In FIGS. 20A to 21, flat plate-like element 111 is separated into anode electrode part 114 and cathode forming part (not shown) by providing insulating resist part 113 after forming a dielectric oxide coating film layer by roughing the surface of anode member 112 made of an aluminum foil serving as a valve function metal (valve metal). Then, by successively laminating and forming a solid electrolyte layer made of a conductive polymer and a cathode layer including a carbon layer and a silver paste layer on the dielectric oxide coating film layer of the cathode forming part, cathode electrode part 115 is formed. Thus, there is provided flat plate-like element 111 provided with anode electrode part 114 and cathode electrode part 115 on both the sides in the longitudinal direction with respect to resist part 113.
Anode com terminal (anode terminal) 116 is provided with plane part 116a so as to form connecting part 116b by bending upward both the ends of plane part 116a. With anode electrode parts 114 of a plurality of elements 111 laminated mounted on plane part 116a of anode com terminal 116, connecting parts 116b are bent inward so as to tightly wrap anode electrode parts 114. The tip portions of connecting parts 116b and anode electrode parts 114 of elements 111 are joined by laser welding of welding parts 116c. 
Cathode electrode part 115 is mounted on plane part 117a of cathode com terminal 117 such that plane part 117a of cathode com terminal 117 and cathode electrode part 115, and cathode electrode parts 115 of elements 111 are joined and connected with conductive adhesive 118.
A plurality of elements 111 is covered with insulating exterior resin 119 with anode com terminal 116 and cathode com terminal 117 connected therewith exposed partially to the outer surface.
By bending portions of anode com terminal 116 and cathode com terminal 117 exposed from exterior resin 119 along exterior resin 119 toward the bottom surface, there is provided a surface mounting type solid electrolytic capacitor with anode terminal part 116d and cathode terminal part 117b formed in the bottom surface part.
The conventional solid electrolytic capacitor of such a configuration enables stable welding work by the laser welding by directing laser beams simultaneously to the tip of connecting part 116b provided in anode com terminal 116 and anode electrode part 114 of element 111.
As the background art document information in relation to the present invention, for example, Unexamined Japanese Patent Publication No. 2003-289023 is known.
However, according to the above-mentioned conventional solid electrolytic capacitor, anode electrode part 114 of element 111 and anode com terminal 116 are joined by laser welding by directing laser beams simultaneously to the end face of connecting part 116b provided to anode com terminal 116 and anode electrode part 114 of element 111. Therefore, as a first problem, it is difficult to carry out the welding work by providing an equal quantity of heat to all laminated elements 111 because of partial escape of the quantity of heat at the time of welding, to anode com terminal 116 via connecting part 116b. Therefore, even though the welding strength is ensured, because of generation of irregularity in the welded state, the ESR was deteriorated due to the presence of a too-much-welded portion or a portion insufficiently welded.
Moreover, as a second problem, since the dielectric oxide coating film layer is formed on the surface of anode electrode part 114 of element 111, irregularity can easily be generated in the welding work. Therefore, as shown in detail in FIG. 22, the lower layer of elements 111 laminated in plurality can hardly be welded, so that the entirety can hardly be welded evenly, and thus the ESR was increased.
Moreover, as a third problem, sputter may be generated at the time of welding by laser mentioned above, and the generated sputter is scattered in the periphery. Therefore, if the above-mentioned sputter is scattered onto insulating resin part 113 provided for the insulation between anode electrode part 114 and cathode electrode part 115, the insulation property deteriorates, and thereby, the ESR is increased. In the worst case of having a large size of, or a large amount of, sputter scattered onto insulating resin part 113, there was a risk of short-circuit due to the breakage of insulation between anode electrode part 114 and cathode electrode part 115.
Next, the periphery of the cathode electrode will be discussed.
FIG. 23 is a perspective view showing the configuration of a conventional solid electrolytic capacitor of this kind, and FIG. 24 is a plan view showing the configuration of an element to be used for the solid electrolytic capacitor. In FIGS. 23 and 24, first, after forming a dielectric oxide coating film layer by roughing the surface of an anode member (not shown) made of an aluminum foil serving as a valve function metal, insulating resist part 122 is provided so as to be separated into anode electrode part 123 and cathode forming part (not shown). Thereafter, by successively laminating and forming a solid electrolyte layer made of a conductive polymer and a cathode layer including a carbon layer and a silver paste layer on the dielectric oxide coating film layer of the cathode forming part, cathode electrode part 124 is formed. Thus, there is provided flat plate-like element 121 provided with anode electrode part 123 and cathode electrode part 124 via resist part 122 in the longitudinal direction.
Anode electrode parts 123 of a plurality of elements 121 mounted on anode com terminal 125 are joined by means of laser welding or the like.
Bent parts 126a are formed by bending upward both the sides of the element mounting portion of cathode com terminal (cathode terminal) 126. The element mounting portion of cathode com terminal 126 and cathode electrode part 124 of element 121, and each cathode electrode part 124 of elements 121 are joined with a conductive adhesive (not shown). Furthermore, the above-mentioned bent part 126a and cathode electrode part 124 are electrically connected with conductive adhesive 127.
The plurality of elements 121 is covered integrally with insulating exterior resin 128 with the above-mentioned anode com terminal 125 and cathode com terminal 126 are both exposed partially to the outer surface. By bending portions of anode com terminal 125 and cathode com terminal 126 exposed from exterior resin 128 along exterior resin 128 toward the bottom surface, a surface mounting type solid electrolytic capacitor with the anode terminal part and the cathode terminal part formed in the bottom surface part is provided.
According to the conventional solid electrolytic capacitor of such a configuration, bent parts 126a are provided by bending upward both the sides of the element mounting portion of cathode com terminal 126, and bent parts 126a and cathode electrode parts 24 of elements 121 are connected with conductive adhesive 127. Thus, since the internal resistance of the entirety at the time of laminating elements 121 can be reduced, low ESR can be achieved.
As the background art document information in relation to the present invention, for example, Unexamined Japanese Patent Publication No. 2003-74753 is known.
However, according to the conventional solid electrolytic capacitor described with reference to FIGS. 23 and 24, low ESR is achieved by reducing the internal resistance by connecting cathode electrode parts 124 of a plurality of laminated elements 121 and bent parts 126a of cathode com terminal 126 via conductive adhesive 127. However, as a fourth problem, since the ESR value of the element 121 main body is high, a problem occurs that a further lower ESR demanded from the market cannot be sufficiently achieved. The reason therefor will be explained hereinafter with reference to FIG. 25.
FIG. 25 is a plan view showing a main part of the process of forming a solid electrolyte layer of conventional element 121 by electrolyte polymerization. In FIG. 25, insulating resist part 122 is first formed on anode member 129 prepared by blanking into a predetermined shape an aluminum foil with the surface roughened and a dielectric oxide coating film layer formed. Resist part 122 separates anode member 129 into anode electrode part 123 and cathode forming part 130. Then, power supply tape 131 is attached to form an electrode for supplying power to the above-mentioned anode member 129. By the electropolymerization by soaking the same into a polymerization vessel (not shown) filled with a polymerization solution and supplying power via power supply tape 131, a solid electrolyte layer made of a conductive polymer is formed on the surface of cathode forming part 130.
Since the production of the solid electrolyte layer in the above-mentioned electropolymerization proceeds along the current flow supplied to cathode forming part 130 via power supply tape 131, the solid electrolyte layer is formed in the order of points A, B, and D shown in the figure.
Therefore, for obtaining a solid electrolyte layer of a desired film thickness, the electropolymerization should be carried out until point D has the desired film thickness. However, at the moment when point D has the desired film thickness, points B and A have a film thickness thicker than that of point D. Therefore, variation in the film thickness of the solid electrolyte layer is generated in cathode forming part 130, so that unnecessary resistance is increased at a portion formed to a film thickness more than necessary, and thus a problem of ESR deterioration occurs.
An object of the present invention is to solve the various kinds of problems of the conventional configurations by providing a solid electrolytic capacitor capable of easily obtaining a stable welded state in the anode electrode part, and suppressing variation in film thickness of the solid electrolyte layer in the cathode forming part, thereby restraining the ESR deterioration to realize the low ESR.